1. Field of the Invention
The present invention relates to an information recording medium for optically recording or reproducing information, and an information recording and reproducing apparatus for recording or reproducing information on the information recording medium.
2. Prior Art
Optical disks are known, such as compact disks and magnetooptical disks, which optically record information by changes in the reflectance factor or changes in the polarization direction of reflected light, for example. A track 261 is formed in a spiral form on the surface of an optical disk as shown in FIG. 26. Along this track on the optical disk, information marks caused by the changes in the reflectance factor or the changes in the polarization direction of the reflected light are formed to record information on a surface of an optical disk 260.
A circuit of the track 261 is divided into an integral number of blocks 262. Each block 262 is divided according to a predetermined disk format into a plurality of areas, on each of which user data and control information for use in recording or reproducing user data is recorded. The blocks are also called sectors.
As an example of disk formats, the format of a rewritable magnetooptical disk 130 mm in diameter and with a recording capacity of 1.3 GB, standardized by ISO (International Standardization Organization) will be described with reference to FIG. 25. In FIG. 25, the numbers given below the information areas denote the numbers of bytes of the related items of information.
The capacity for one block (sector) 262 is 1410 bytes. One block includes at its leading end a preformatted header segment 250 of 63 bytes. In the format of FIG. 25, information in the preformatted header 250 is recorded with information marks consisting of prepits formed at the time of manufacture of the optical disk. Information other than that in the preformatted header segment 250 is not preformatted, but is recorded with rewritable information marks.
The preformatted header segment 250 includes a sector mark segment (SM) 256 to record information to indicate the leading end of this block, a VFO segment 257, an address mark segment (AM) 258, an address information segment (ID) 259, and a PA segment 267. The address information segment (ID) 259 has recorded therein information to indicate the location of this block 262 on the optical disk 260, and has a self-clocking function to generate a clock signal from its own information during reproduction. The VFO segment 257 has recorded therein information to designate a specific frequency for pull-in when generating a clock signal for the address information segment 259. The AM segment 258 has recorded therein information to indicate that there is an address information segment (ID) 259 in the subsequent segment. In each preformatted header, a VFO segment 257, an AM segment 258, and an address information segment 259 are arranged twice in succession, and the PA segment 267 is provided to adjust the length of the information marks in the whole area of the preformatted header segment 250.
Behind the preformatted header segment 250, an ALPC-GAPS segment 251 is provided. The ALPC-GAPS segment 251 includes a FLAG segment 265 to show whether or not data has been recorded in a data field 254, an ALPC segment 266 for recording information to control the power of the laser in recording, and GAP segments 264 as buffer portions placed between the segments.
Following this, a data field 254 for recording user data is provided. The data field 254 also has a self-clocking function. Before the data field 254, a VFO segment 252 and a SYNC segment 253 are provided. In the VFO segment 252, a specific frequency is recorded for pull-in for generating a clock signal in synchronism with data when reproducing data from the data field 254. In the SYNC segment 253, information about timing for demodulating information during reproduction is recorded.
In the data field 254, RESYNC segments 268 and data segments 267 are alternately provided. The RESYNC segments 268 are provided to re-attain synchronism when loss of synchronism occurs between data and clock during the self-clocking operation. Data 267 consists of information 1040 bytes long, which includes user data of 1024 bytes, a CRC segment to check if user data is read correctly, and a DMP segment to show where error data is when error data occurs due to corruption of data, and ECC codes of 160 bytes added to correct the error data. When recording, two bytes of RESYNC 268 are added for every 30 bytes of data 267.
In the rear of the data field 254, a buffer segment 255 is provided. The clock for recording information has a fixed frequency, and therefore when a variation occurs in the rotating speed of the motor to drive the optical disk or when the center of the track 261 deviates from the center of rotation, the linear velocity of the laser beam for writing on the track 261 varies, but the buffer 255 absorbs this variation.
In the conventional format standardized by ISO, in one block 262 of 1410 bytes, the user data capacity at which the user can record data is 1024 bytes in the data field 254. Therefore, the recording efficiency of user data is 1024/1410, namely, 72.6%. The remaining 27.4% is accounted for by the address information segment 259 and control signals of VFO segments 257, 252, when reproducing so that the recording efficiency of user data is not so high.
For this reason, to improve the recording efficiency of user data, JP-A-49-103515 discloses a technique by which the track is made to fluctuate with minute waves, and address information of the track is recorded by the variation of the frequency of the waves. Specifically, the track is formed during the manufacture of the optical disk such that the center of the track is made to fluctuate minutely (by wobbling) in the width direction of the track, the frequency of this wobbling is varied along the longitudinal direction of the track, by which the address information of the track is represented. Since the address information is recorded by the wobbling of the track, it is not necessary to record the address information with the information marks, and accordingly the area for recording user data with the information marks can be increased. Thus, the recording efficiency of user data can be enhanced.
However, the above technique in JP-A-49-103515 is unable to use a track width smaller than the diameter of the beam spot of the laser beam in reproduction. The reason for this is that if the track width is narrower than the beam spot, the leakage of information from adjacent tracks increases, making it difficult to reproduce information correctly.
In literature titled International Symposium on Optical Memory 1995 (ISOM '95) TECHNICAL DIGEST Fr-D4 "A NEW DISC FOR LAND/GROOVE RECORDING ON AN MSR DISC, a land/groove track structure was proposed in which, as shown in FIG. 1, grooves 3 are formed mutually separated by a fixed space on the surface of the optical disk, and while those grooves 3 are used as tracks, lands 2 between the grooves 3 are also used as tracks. In this structure, since the tracks on the lands 2 are adjacent to the tracks in the grooves 3, there is a level difference corresponding to the depth h between the adjacent tracks. Therefore, as shown in FIG. 1, the diameter of the reproducing beam spot 1 of the laser beam is larger than the track width in the reproduction process, and also when the reproducing beam spot 1 extends over the adjacent tracks on both sides of the track from which data is reproduced, with the phases of reflected beams from the adjacent tracks, a phase difference corresponds to the difference in the height h of the tracks, thus making it possible to prevent the leakage of information from the adjacent tracks. Therefore, the track width can be made smaller than the beam spot diameter, so that the track density can be increased. Also in this literature, as shown in FIG. 1, another technique was revealed in which the border between the land 2 and the groove 3 is made to wobble, and address information is recorded with the wobbling frequency. Also, a structure was proposed in which the track width is smaller than the reproducing beam spot, and there are always two borders between the land 2 and the groove 3 within the reproducing beam spot 1, and therefore address information is represented by wobbling only one of the two borders.
However, in the structure in that literature as shown in FIG. 1, since the part wobbles is the border between the land and the groove, the wobbling motion of the border is shared by the track on the land side and the track on the groove side. Therefore, not only when the center of the reproducing beam spot 1 is located on the land side 2 but also when the beam spot is located on the groove side, the wobbling motion of the same border is detected, and accordingly address information specified by the wobbling frequency is produced. Hence, it is impossible to decide from the address information reproduced by wobbling whether the reproducing beam spot 1 is on the track of the land side 2 or on the track of the groove side 3. If for some reason the tracking servo fails to keep track and the reproducing beam spot shifts to the adjacent track, this cannot be detected from address information, with the result that there is a possibility that information of the adjacent track is reproduced and recorded by mistake.